pick_address: Warn and continue when you find at least 1 IPv4 or IPv6 address

pick_address: Warn and continue when you find at least 1 IPv4 or IPv6 address

Currently if specify a single public or cluster network, yet have both
`ms bind ipv4` and `ms bind ipv6` set daemons crash when they can't find
both IPs from the same network:

    unable to find any IPv4 address in networks '2001:db8:11d::/120' interfaces ''

And rightly so, of course it can't find an IPv4 network in an IPv6
network.
This patch, adds a new helper method, networks_address_family_coverage,
that takes the list of networks and returns a bitmap of address families
supported.
We then check to see if we have enough networks defined and if you don't
it'll warn and then continue.

Also update the network-config-ref to mention having to define both
address family addresses for cluster and or public networks.

As well as a warning about `ms bind ipv4` being enabled by default which
is easy to miss, there by enabling dual stack when you may only be
expect single stack IPv6.

Thee is also a drive by to fix a `note` that wan't being displayed due
to missing RST syntax.

Signed-off-by: Matthew Oliver <moliver@suse.com>
Fixes: https://tracker.ceph.com/issues/46845
Fixes: https://tracker.ceph.com/issues/39711